Power to weight ratio units?

[Visitor Q]

Hi guys, was just wondering what the general forumla and unit for the power to weight ratio of a bike/ car would be so i can feel smug when telling chavs why my 'little' 350 will demolish them from the lights in their little novas.

I would imagine it would be weight / bhp ergo

R1 = 1 because it is 180kg / 180 bhp

My bike would be 145kg / 32 = 4.531

Etc

Altho im not sure which way it would be done, what unit, etc etc. Any help?
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[McJamweasel]

Nope.

Power/Weight. So more like 32/145 = 0.22 bhp/kg.
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[Visitor Q]

[Dr Nick]

[McJamweasel]

Very true Nick. According to the factory claims, the R1 do indeed have 1 bhp/kg - however so does the ZX10. When you take into account the bollocks that the factories claim, however, both fall short.
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[Visitor Q]

Yes but no doubt you would work it from the crank cos bearing in mind the wet weight would add on about 20 kg usually (give or take) so just take the easiest to measure. Rear wheel bhp will have lots to do with chain, sprocket, tyre etc... Crank at least will be consistent.

I dunno. its all too confusing
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From September 2014 to January/February 2015 I will not be using any English, nor reading any. As such, I won't be on here. PM at will, but I won't be checking/posting unless in emergencies. Certainly not for the first couple of months. Please berate me savagely if I break that rule...

[McJamweasel]

Consistent? Maybe, but of very little value in the real world.
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[Visitor Q]

true BUT bear in mind an R1 with a 150kg lisa riley squatting on it is gonna have a worse power to weight then an R6.

Not to mention the aerodynamics.

However we arent taking that into account are we.

Simple ball park figures are the best way to do things.
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China traffic/travel bike vid - When I make a sweeping statement, please add the word 'statistically' in to the sentence before you bitch...
From September 2014 to January/February 2015 I will not be using any English, nor reading any. As such, I won't be on here. PM at will, but I won't be checking/posting unless in emergencies. Certainly not for the first couple of months. Please berate me savagely if I break that rule...

[MarJay]

Its a ratio... technically it has no units!

I mean fancy saying bhp per Kg... thats an imperial versus a metric unit!

Ratios don't have units, they are just for comparison purposes. EG, Yamaha R1 claimed weight 176kg, claimed power 176bhp. Power to weight ratio of 1.

Triumph Daytona 955i. Claimed power 147bhp, claimed weight 189kg. Power to weight ratio of 0.78.

R1 has greater power to weight ratio than Daytona.

Thats the only use that a Ratio has. Ratios are never expressed with units.

I'm sorry if that rambled a bit, but I have just done a 12 hour shift with no breaks and no food.
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[Mr C]

of course you have to specify units

you can only have a real ratio if you are comparing apples and apples - if not then you have to specify units


the R1 has a 1:1 ratio (pffffft yeah right )

anyhow

let's let them have that for now and say that a mythical R1 has 180bhp and weighs 180kg

so it has a power to weight ratio of 1 (no units)

no it doesn't

it has a power to weight ratio of 1 bhp per kg

or 133kW per 6349 ounces

or 735Nm/s per 3.54cwt

and so on

none of these are unity apart from the arbitrary ratio chosen

so no, power to weight ration can't be expresed without units at all
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187.3bhp = 201mph

[Frost]

power to weight also must be taken with a pinch of salt, especially when compairing bikes to cars. take a 180kg bike, and calculate its power to weight ration, then plonk a 90kg fatass on it and all your statistics are utterly ballsed up. slap the same fatass in a 1 tonn car and his weight will make less of an impact on the figures.

power to weight cant allways be used to determine which vehical is faster as drag is not taken into account.

typically bikes wipe the floor with everything power to weight wise, untill you put a rider ont he bike at which point they become the more powerful by a slimmer margin. Bikes still own 99% of cars though

[Adam_P]

The best way to impress the chavs would be to work it out in bhp per ton (tonne?) That way, it will work along the same lines as their car power to weight ratios, and you'll walk all over them!

For instance, the Caterham R500 is quoted as having 500bhp per tonne, that's because the car weighs less than a tonne, but the power output ratio (this is where Marjey's ratio bit comes in to it!) would work out to this figure if it did.
A bik weighs the better part of sod all, so whatever it is, it'll be a damn sight better than a max powered nova, especially with all the filler and extra weight they carry with speakers, amps, bodykits and obligatory tracksuit bottom wearing/McDonalds eating girlfriend.

However, I haven't the faintest idea how to do the maths to get to the figures. But, I'm sure someone will. It sounds like Mr C does already!
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[mchaggis]

In which case, your mythical R1 has a power to weight ratio of 1000 bhp per ton. Beats the pants of pretty much any car. There are special cases, with F1 cars, 940ish bhp in a 600 kg car, gives you about getting on for 1600 bhp per tonne.

The Clio 172, 172hp per 1055kg gives you a poxy 163 bhp per tonne. A CG125 probably has getting on for 100 bhp per tonne... Chav's eh.. stick that up them.

[Frost]

[Robby]

Working in bhp/kilo because its more relative to bikes:

Roughly:

1.0 Nova. About 45bhp and 800kg. So it has 0.056 bhp/kilo

1.3 golf. 60bhp and 880kg going by haynes. 0.068 bhp/kilo. I had one of these. They're slow.

2.6 merc. 160bhp and 1200kg. 0.133 bhp/kilo. In car terms thats not bad.

To compare against some small bikes:

NSR125. 24bhp, about 140kg. 0.171 bhp/kilo. Still poor. Pissy little 125s.

GS500. 50bhp, about 170kg. 0.294 bhp/kilo.

CBR600. 95bhp, about 180kg. 0.52 bhp/kilo.


Then above this the weight stays the same or gets less, and the power just shoots up. Big power in the litre class bikes. As much as my car, and that like to spin its wheels and kick hard when you poke it.

[G]

[byke95]

[Bendy]

bhp per £1 is sometimes quite interesting too.

Lets just say, my Micra kicked my CBR's ass on that front.

Hey, I had to let the Joy Machine win on something, it weighed three and half times what my bike does and put out less than half the power. Bless it.

[Mr C]

and that one is an exponential scale

more and more money for less and less performance improvement
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187.3bhp = 201mph

[Fat Controller]

Take a secondhand bike into the equation and it gets even sillier! This is quite a good line but no-one has mentioned adding torque into the equation yet.

bhp at crank/dry weight multiplied by torque

Oh and while we are at it why not add in faired or non faired i.e wind resistance.

Still with me riding it'd go nowhere!!
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